This invention relates to controller technologies, and in particular, to a digital controller in which two control paths having different digital converters are utilized to generate a control signal.
Because of its numerous advantages such as programmability, flexibility, immunity to noise and ease of integration, a digital controller is widely used to regulate an output of, for example, a power converter system (such as a lamp driver, motor driver, voltage regulator, etc.). As shown in FIG. 1, the digital controller 10 comprises an analog-to-digital (A/D) converter 11 to sense a signal Vsense, such as the regulated output voltage of the power converter. The digital output of the A/D converter 11 is then sent to a feedback compensation unit 12 (e.g., micro-controller or programmable logic circuit such as FPGA or CPLD) to implement the feedback compensation function in accordance to a reference Vref, so as to stabilize the feedback loop. An output signal is generated by a signal generator 13 to control the power switches of the power converter to regulate the output voltage.
For most applications, the bandwidth of the system shown in FIG. 1 is limited by the sampling speed of the A/D converter 11. For a system requiring higher resolution and bandwidth, the power consumption of the controller increases significantly. For example, a 10-time-speed improvement in the A/D converter 11 could increase the power consumption of the A/D converter 11 by 3-5 times. Therefore, a high-speed high-resolution A/D converter is high power consuming.
In a low-cost application, instead of using an expensive high-speed high-resolution A/D converter, either a high-speed low-resolution or a low-speed high-resolution A/D converter is used. A high-speed low-resolution A/D converter can easily meet the requirement of the dynamic response due to the high bandwidth control, it, however, could have problem with the steady state requirement of the system. On the other hand, a low-speed high-resolution A/D converter can easily meet the requirement of the steady state, but could have problem with dynamic responses.
Therefore, there is a need for a new digital converter resolution which is low in cost and power consumption but is still able to meet both dynamic transient and steady state requirements of the system.
The present invention provides a novel digital controller in which two control paths are employed instead of one. In particular, each control path has an A/D converter and a compensation unit, and the two A/D converters have different sampling speeds and/or resolutions to meet both requirements of dynamic response and steady state. Thus, a costly and high power consumption high-speed high resolution A/D converter can be replaced by a combination of a high-speed low resolution A/D converter and a low-speed high-resolution A/D converter.
Preferably, the sampling speeds of the two A/D converters are substantially different such that the control of the two control paths is de-coupled and will not interfere with each other. The two control paths may sense the same signal source or different digital sources.